One problem related to power assist brake has been reported for the 1999 Chrysler 300M. The most recently reported issues are listed below.
My Chrysler 300m loses its power brakes whenever it is cold and it seems damp out side. The power brake booster seems to be the problem. When the car warms up it works good enough to drive but the brakes are still sluggish. After driving the car for 15 min to half hour the brake booster seems to start working ok. It has done this since I bought the car. I have no braking when the car is cold sometimes! and a loud sucking sound comes out of the brake booster when its hanging up.